1. Field of the Invention
The present invention generally relates to semiconductor structure and method of forming the same, and more particularly, to an isolation structure of a semiconductor structure and the method of forming the same.
2. Description of the Prior Art
In advanced semiconductor technology, fin field effect transistors (Fin FET) have taken the place of traditional planar transistors and have become the mainstream of development. Generally, at the beginning of forming a fin FET, trenches are formed in a semiconductor substrate by patterning processes, such as a photolithograph-etching process (PEP), to transfer the pattern of a design layout to the semiconductor substrate wherein areas of fin structures are defined in the semiconductor substrate by the trenches. Insulating materials are then formed and filled in to the trenches to form an isolation structure between the fin structures. Afterward, gate structures crossing over the fin structures may be formed, and the overlap regions of the fin structures and the gate structures are the channel regions of the fin FETs. To improve device performance, a strained silicon structure may be formed at each side of the gate structures to be the source/drain region.
With the development of semiconductor technology, the sizes of semiconductor devices continue to shrink for better performance, higher degree of integration and better economic benefit. To fabricate the semiconductor devices comprising finer fin structures and small pitches, multiple-patterning technologies have been proposed and widely adopted for better resolution and avoiding the deformation result from etching loading effect, such as photolithography-etch-photolithography-etch (2P2E) process, photolithography-photolithography-etch (2P1E) process or spacer self-aligned double-patterning (SADP) process. For example, as shown in FIG. 1, a first patterning process is carried out to define an array of fin structures 10 on the substrate 1, wherein a plurality of fin structures extending along the same direction are arranged in close proximity to each other and separated by the trenches 20 formed therebetween. Afterward, a second patterning process is carried out, for example, to remove the dummy fin structures 10a and 10b to form wider trenches 21 thereby. Subsequently, a third patterning process may be performed, for example, to form the trenches 22, 24 and 26 to divide the fin structures into fin segments (or sections). After the multiple-patterning processes aforesaid, the trenches 20, 21, 22, 24, 26 may be filled with an insulating material, and a planarization process may then be performed, to remove the excess insulating material and form the isolation structures. The fin segments formed by the multiple-patterning technology may be more uniform in dimensions and may have tapered cross-sectional profiles. Conventional line end shorting or narrowing problem caused by optical proximity effect (OPE) is prevented. The fin segments formed on the substrate by the multiple-patterning technology may have similar cross-sectional profiles regardless of variations in patterning densities and pitches.
However, with the trend of device shrinking, the widths of the trenches may also be scaled down. Regarding the trench used to segment fin structures, such as the trench 24, smaller width may make the adjacent distal ends of two fin segments, such as 10c and 10d, be so close that the risk of epitaxial bridging among them is increased. Similarly, for the purpose of device shrinking, the source/drain contact plugs may be disposed very close to the distal ends of fin segments. Unfortunately, facet defects are found more often in the epitaxial structures near the distal ends of the fin segment and therefore result in poor landing of the source/drain contact plugs.
Therefore, there is still a need in the field to provide an improved isolation structure used in dividing the fin structures into a plurality of fin segments. The isolation structure may preferably have a smaller width to achieve a smaller layout area, and furthermore, may be able to prevent the epitaxial bridging issue between the adjacent distal ends of the closely spaced fin segments and improve the yield of the source/drain contact plugs disposed at the distal ends.